Fiber mixtures are often used to form filter media and other non-woven media. In the formation of these media, fibers are mixed in a variety of ways. The fibers may be dry mixed in air, or other gas, or wet mixed in water, or other liquid. One common difficulty with dry mixing is the build up of a static charge that prevents the fibers from mingling. While the build up of static charge is less problematic in wet mixing this type of mixing has its own hurdles. In wet mixing, the fibers may gather at the surface forming a membrane that floats on the surface with out mixing at depth with fibers contained in the liquid below. The use of electrospun or other fibers that are quenched upon contact with the liquid exacerbates this problem because, as the fibers are quenched at the surface, they form a single tangled membrane. This membrane does not separate to mix with the other fibers.
To force mixing, attempts have been made to agitate the fiber containing slurry with mechanical elements such as an impeller. While this technique provides some relief by drawing the fibers downward within the slurry, the fibers unfortunately wrap themselves around the impeller and its shaft. With the fibers ensorceling the impeller, these fibers are not free to intermingle with the fibers in the surrounding liquid. Similar to the use of an impeller, introducing elements through the surface of the slurry is known to cause the fibers to wrap themselves around these elements. The central problem in each situation is the agglomeration of fibers preventing the mixing of two types of fibers to any depth. In other words, the short fibers are found at the surface of the resultant long fiber membrane without penetration into the matrix of long fibers.